This invention relates to electrical receptacles and particularly to receptacles with a shallow housing also provided with surge suppressor and isolated ground features.
Most duplex electrical receptacles used for residential and commercial applications have a housing, including an insulating base and cover, with a depth dimension for the base of about 1 inch or more to house the contacts and any other internal components. Some receptacles for such applications have a more shallow depth dimension. One such receptacle is the Bryant T-82 receptacle with a maximum base depth of only about 0.7 inch and only about 0.5 inch over most of the base. These receptacles are easily installed in construction boxes having a total depth of only about 1.5 inches. While the basic features for a satisfactory duplex receptacle have thus been provided in a shallow enclosure, the shallowness of the enclosure minimizes the internal volume available for additional features or functional components.
There has recently been a growing interest in providing receptacles with surge suppression. In Misencik et al. U.S. Pat. No. 4,912,590, Mar. 27, 1990, there is disclosed an electrical surge suppressor and dual indicator apparatus for incorporation within receptacles. The surge suppressor of the patent is one example of surge suppressor apparatus that may be utilized in accordance with the present invention within shallow receptacles.
One object of the present invention is to provide receptacle configurations, with surge suppressors, that are suitable even for compact, shallow receptacles.
Grounding is an important feature of most receptacles. Receptacles as. commonly used have an insulating housing with a metal mounting yoke. For duplex receptacles in which each part has three contacts for the pair of line conductors and the ground conductor, it is commonly the case that the ground contacts within the receptacle are conductively related to the metal mounting yoke. A grounding path may exist through the metal mounting yoke to the wall box in which the receptacle is mounted, as well as through a ground conductor connected to the ground contacts. As is well known, it is sometimes preferred that the internal grounding contacts are conductively connected only with a grounding path apart from the metal yoke and wall box. Such an isolated ground has been achieved by providing an insulating barrier between the ground contacts and the yoke. Shallow receptacles, such as the above-mentioned Bryant type SP52L, present a need for isolated ground features that is uniquely satisfied in accordance with a further aspect of the present invention.
The foregoing aspects of the invention, relating to (1) mounting a surge suppressor and (2) the provision of an isolated ground, may of course be used independently of each other as well as in combination. They are described together in the specific embodiment of applicant's invention hereinafter.
Briefly, the invention succeeds in mounting surge suppressor circuits in receptacles, even if they are shallow, by use of an insulating circuit board on which components of the circuit are mounted with board portions that fit in close relation to insulating walls of the receptacle base so it is secure in use while also being easily assembled in the receptacle.
In an embodiment of the invention, the circuit board is centrally located between the two contact areas of the duplex receptacle and on its top surface facing the front cover of the device are mounted the indicator element or elements of the surge suppressor which are viewable from the front of the device when the cover is on. The other components of the suppressor circuit are located on the back side of the circuit board within a pocket of the base. The circuit board is mounted on respective notched wall portions in which elements such as first and second lateral ears of the circuit board fit to avoid movement of the board. Further, there is provided support under the board by part of the insulating wall portion and the cover may assist in clamping the board in place.
The circuit board may be configured to have most of its working elements closely bonded to the circuit board itself while one or more metal oxide varistors, which provide the key surge suppression functions in the circuit, are physically located spaced from the circuit board, attached thereto by conductors to complete the circuit, in the volume located below the circuit board and its more closely mounted components.
To provide the isolated ground of a receptacle, which may be shallow in its housing configuration, the two sets of contacts each include a pair of power contacts and a ground contact in which the ground contact has a length that extends into a bottom projection of the base. Ground contacts are normally longer in extent than power contacts because the mating plug has a longer ground prong. In shallow receptacles, it may not be possible to configure the housing to provide the ground contact within the depth that accommodates the power contacts Thus, the base of a device such as the Bryant SP52L is provided with two bottom projections that each provide a cavity for each ground contact. According to this invention, each such bottom projection has an opening allowing external access to the ground contact contained therein and a ground conductor is connected to each such ground contact. Each ground contact is free of any connection to the mounting yoke.
In one embodiment, the ground conductor is a metal bar or strap to which each of the ground contacts is directly fastened such as by a rivet. The metal bar slides in place through a slot defined by parts of the insulating housing of one housing projection and into a pocket of the other housing projection. A flexible conductor is bonded to the metal bar for joining to a separate conductor to ground.
In a further embodiment, the housing and metal ground bar as described above are provided in combination with an insulating cover that shields the ground bar against inadvertent contact with other grounds. The cover for the ground bar is configured, in one form, so it also serves as a strain relief protecting against breakage of the connection of the flexible ground conductor with the ground bar.
The cover may be used with or without the ground bar as a way to provide an assembly with an increase space for varistors of the surge suppressor circuit. In the latter case, the use of the back cover allows the bottom wall of the housing to have an opening so components of the surge suppressor can occupy more space. This is especially helpful for allowing use of more varistors in the surge suppressor, even though the back cover extends substantially only to the depth of the housing projections that accommodate the ground contacts.
These and other aspects of the present invention will become more apparent with reference to the following description and drawings.